The present disclosure relates to medical probes, and more particularly, the present disclosure relates to medical probes, such as catheters, in which a fluid is transported within a portion of the probe.
Medical probes, such as catheters, are commonly used in minimally invasive procedures for the diagnosis and treatment of medical conditions. Such procedures may involve the use of intraluminal, intracavity, intravascular, and intracardiac catheters and related systems. When performing such procedures, imaging and treatment catheters are often inserted percutaneously into the body and into an accessible vessel of the vascular system at a site remote from the vessel or organ to be diagnosed and/or treated. The catheter is then advanced through the vessels of the vascular system to the region of the body to be treated.
The catheter may be equipped with an imaging device employing an imaging modality such as optical imaging, optical spectroscopy, fluorescence, infrared cardiac endoscopy, acoustic imaging, photo-acoustic imaging, thermography, and magnetic resonance imaging. For example, an ultrasound or optical imaging device may be employed to locate and diagnose a diseased portion of the body, such as, a stenosed region of an artery. The catheter may also be provided with a therapeutic device, such as those used for performing interventional techniques including balloon angioplasty, laser ablation, rotational atherectomy, directional atherectomy and the like.
Imaging catheters, such as intravascular and intracardiac ultrasound catheters, typically require the catheter body to be purged of air during operation. The purging is performed to support the efficient propagation, within the catheter body, of imaging energy generated or detected by one or more internal transducers. For example, an ultrasound transducer housed within an intravascular ultrasound catheter is typically immersed in a liquid during operation to support the efficient coupling of acoustic waves from the transducer to the external medium to be imaged.
The fluid is commonly introduced into the catheter by a procedure referred to as “flushing” the catheter, where fluid is injected into the catheter via a port at the proximal end. This fluid, which is typically a liquid such as saline or sterile water, travels along the length of the inner main lumen of the catheter and purges air out of a port near the distal tip of the catheter. Other catheters do not support flushing of the catheter through ports available outside the body. Such catheters typically require manual injection of a fluid coupling medium to the distal tip of the catheter via a needle attached to a syringe. It is desirable to making flushing a safe, simple, quick and effective procedure. In many applications, it is also desirable to fluidly isolate inner portions of catheters from the anatomic environment into which they are used. Generally, the catheter is flushed with liquid prior to insertion of the catheter into the vasculature if the physician wishes to minimize the probability of introducing air bubbles into the bloodstream.
Many intravascular imaging catheters are designed such that, during use, blood can enter the catheter via the distal flushing port. This blood can interfere with the mechanical or imaging performance of the catheter. For example, if the blood were to form a thrombus within the imaging catheter, it could damage delicate components within the catheter and/or be expelled during a subsequent flushing procedure, potentially leading to embolic complications. Furthermore, the use of a distal flushing port that potentially releases particles or soluble materials from inside the catheter into the vasculature reduces design flexibility with respect to the selection of materials used within the catheter. It also requires that the fluid used for flushing be physiologically compatible, such as saline.
In some cases, a catheter may be inadequately flushed, and the resulting imaging quality can be significantly degraded. For example, air bubbles on ultrasound transducers or optical components substantially reduce image quality if they lie within regions in which acoustic waves or optical energy travel.
As an alternative to flushing via a proximal port and allowing fluid to exit via a distal port, some catheters have been designed with a separate lumen as part of the imaging catheter to deliver fluid to the distal end of the catheter, allowing the fluid to “backfill” the main lumen of the catheter. Alternatively, the separate lumen can used as a venting lumen, where the fluid is introduced via the main lumen, and the separate lumen allows air to escape.
The separate flushing lumen takes up space and is often made as small as possible to avoid an excessive increase in the diameter of the catheter. This can unfortunately be a significant limitation in the case of intravascular catheters, which typically require a compact configuration in order to enable delivery into the vasculature. For example, catheters currently employed for intravascular ultrasound and intracardiac echocardiography are approximately 0.8 to 4 mm in diameter, where the smaller sizes of probes can be delivered more distally within the vascular tree of the coronary anatomy as the vessel caliber tapers down or as diseased vessels are stenosed. Furthermore, such probes may be advanced across the atrial septum from the right atrium into the left atrium of the heart via either a pre-existing communication, such as a patent foramen ovale, or via a communication created during a procedure, such as a trans-septal puncture. Smaller sizes generally allow for interrogation of a larger portion of the coronary or cardiac anatomy or may allow for the creation of smaller holes through which to access the desired anatomic regions. It is therefore desirable for a probe and its components to be contained within a minimal outer diameter or minimal cross-sectional area to enable imaging.